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Gravitational Learning Objectives

Content

• Concept of a force field as a region in which a body experiences a non-contact force.
• Students should recognise that a force field can be represented as a vector, the direction of which must be determined by inspection.
• Force fields arise from the interaction of mass, of static charge, and between moving charges.
• Gravity as a universal attractive force acting between all matter.
• Magnitude of force between point masses: F = Gm₁m₂/r² where G is the gravitational constant.
• Representation of a gravitational field by gravitational field lines.
• g as force per unit mass as defined by g = F/m
• Magnitude of g in a radial field given by g = GM/r²
• Understanding of definition of gravitational potential, including zero value at infinity.
• Understanding of gravitational potential difference.
• Work done in moving mass m given by ∆W = m∆V
• Equipotential surfaces.
• Idea that no work is done when moving along an equipotential surface.
• V in a radial field given by V = − GM/r
• Significance of the negative sign.
• Graphical representations of variations of g and V with r.
• V related to g by: g = − ∆ V/∆ r
• ∆ V from area under graph of g against r.
• Orbital period and speed related to radius of circular orbit; derivation of T² ∝ r³
• Energy considerations for an orbiting satellite.
• Total energy of an orbiting satellite.
• Escape velocity.
• Synchronous orbits.
• Use of satellites in low orbits and geostationary orbits, to include plane and radius of geostationary orbit.

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